Constant torque clutch



July 7, 1953 J. RABINOW 2,644,393

CONSTANT TORQUE CLUTCH Filed Dec. 17, 1947 4 Sheets-Sheet 1 awe/rm I I Jacob 'Ra'lm'nnw y 7 1953 v J. RABINOW 2,644,398

CONSTANT TORQUE CLUTCH Filed Dec. 17, 1947 4 Sheets-Sheet 2 TURBINE I 1 4 IE I E1 8 GENERATOR 48 7 GEAR RsDucT/ON \SETTING D/HL SETMBLEGMR [2 v I'DLER 5 44 muowzk PLATE cvlvsmA/r-ronoug TORQUE k9: lurch,

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- ESC'HPE'MA'IVT Disc LEVER July 7, 1953 .1. RABINOW CONSTANT TORQUE CLUTCH 4 Sheets-Sheet 3 Filed D60. 17, 1947 Janp b Rehab-113w y 7, 1953 J. RABINOW 2 644,398

CONSTANT TORQUE CLUTCH Filed Dec. 17, 1947 4 Sheets-Sheet 4 Jana]; DW A Patented July 7, 1953 CONSTANT TORQUE CLUTCH Jacob Rabinow, Washington, D. 0., assignor to the United States of America as represented by the Secretary of the Army Application December 17, 1947, Serial No. 792,252

Claims;

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

My invention relates to safety arming mechanisms for fuzes and particularly to an arming mechanism for electrically-actuated bomb fuzes,

said arming mechanism having a time delay mechanism adapted to control the time of arming of said fuze. More specifically my invention relates to means for utilizing a variable force driving Source such as a wind vane to provide a constant torque for driving an escapement mechanism to provide a definite, controllable time delay for a fuze arming mechanism.

My invention is applicable to any projectile fuze of the mechanical or electrical type for which safe operation requires that the projectile remain in the unarmed condition until a predetermined interval after it is released; the invention is particularly applicable to electrically actuated bomb fuzes in which an electric squib is fired to set off the fuze and it will be disclosed in connection with such a fuze although it will be understood that it is equally applicable to any other type of fuze employing a wind vane or turbine.

So-called air travel arming has long been used for projectile fuzes. In this type of device a wind vane or turbine is so associated with the arming device that after a predetermined number of turns of the wind vane due to travel of the projectile through the air, the fuze is in the armed condition. One important objection to this type of arming is that the time required to complete the arming depends on the velocityof the projectile during the arming period, and this is different for different sizes and types of projectiles such as bombs and rockets. As it is desirable to use one type of fuze for more than one type or size of projectile, it will be seen that the arming time is not necessarily a definite quantity with air-driven type of arming. The arming time with this type of device will also vary with the horizontal initial speed of the projectile. It has therefore been proposed to use a spring driven clock mechanism, and such mechanisms have been developed, but they lack the essential safety of air travel mechanism in that they may operate if defective even when the projectile is not in flight.

If the Wind vane is used as a power source to drive a generator, as is the case in some types of electric fuzes, driving a clock mechanism directlyfrom the wind vane shaft does not al- (Granted under Title 35, U. S. Code sec. 266) i ways supply suitable torque to the clock mechanism, since the wind vane speed may vary widely and in this case the torque will also vary so that it is difficult to obtain a desired accuracy of timing. As the generator requires a highspeed drive, considerable gearing down is necessary to drive the clock work. Such direct operation of slow-speed clock work from a highspeed shaft through gearing results in large forces on the clock mechanism which makes it diificult to secure good operation. If the wind vaneis not used for other purposes, it may be designed so that it will be slowed down by the clock work without producing excessive forces, and therefore may be used to drive the clock work directly.

It is an object of my invention to secure accuate time arming (as against air travel arming) by the use of a clock work timing mechanism driven from the high speed turbine shaft, the above mentioned and other difficulties being obviated when the wind vane is also used to drive a generator, by the use of a novel constanttorque clutch which slips whenever a predetermined torque is exceeded.

Other objects are to provide a fuse arming mechanism that can be used with existing types of fuzes; that is readily adjustable as to timing; that can be inexpensively constructed of simple and readily available parts; and that is reliable and foolproof in use and operation.

Other objects and advantages will be apparent from the following description and drawings in which:

Fig. l is a longitudinalview partly in cross section of a projectileembodying my invention,

Fig. 2 is an enlarged longitudinal sectional detailed view of the fuze,

Fig. 3 is an exploded schematic diagram of the essential elements of my invention showing I the principle thereof,

Fig. 4 is a view of partial section taken on line 4-4 of Fig. 5,

Fig. 5 is a sectional detailed view taken on line 5-5 of Fig. 2,

Fig. 6 is an enlarged detailed sectional view taken on line 6--6 of Fig. 4, of the planetary setting gear showing its cooperation with the setting dial,

Fig. 7 is a detailed sectional view taken on lines11 of Fig. 4 of the latch mechanism immediately after the latch has been released,

Fig. 8 is an enlarged sectional view of the preset catch taken on line 88 of Fig. 7 in the initial safety position,

Fig. 8a is a view similar to Fig. 8, showing the catch actuated by the safety arming pin,

Fig. 9 is a schematic diagram of one circuit which may be employed in the electric fuze; and

Fig. shows a modification in which a clock mechanism is driven directly from 'a wind vane shaft.

Referring to the drawings, a projectile I, carrying the usual explosive charge, is provided with fuze 2, which may be of any type, but which is shown as an electric fuz'e of any-known type. The fuze shown is provided with an aperture 3 for admitting an air stream to wind vane or turbine 4 which is thereby caused to rotate-When the projectile is in motion. The air escapes througha series of peripheral exhaust ports *5. Turbine 4 drives shaft I which is supported in bearings la, lb, and, in turn, drives a generator indicated at B in Figs. 1 'and 3. The generator serves to supply power to the electric circuits of the fuze which may 'be housed, with the construction shown, in the annular space 9, al-' though this arrangement is not material to my invention.

Shaft 7 terminates in worm H which drives gear l2; this, in turn, drives idler 14 through spiral gear [3 to provide a suitable speed reduction. Idler l4 rotates freely on the shaft 19 of shaft and gear assembly [9, 2|, '3! andconstitutes the driving elementof my constant-torque clutch in that it bears upon the follower friction plate 16, and tends 'to rotate the latter with it. The follower friction plate It is threaded'on shaft l9 and is urged by torque spring [8 in such direction of rotation as tends'to make it bear against idler l4, while the torque transmitted to the follower frictionplate from idler I4 tends to drive the plate away from the idler whenever mal speed. Both of these undesirable effects are eliminated by using the constant torque clutch. However, thereare'als'o applications in: which no generator is employed and where the it causes relative motion betweenthe idler and shaft IS on which it is threaded; this of course occurs only when thereis slippage between idler I4 and friction plate It, whichihappens whenever.

the torque of spring I8 is exceeded. The other end of torque'spring I8 is fixed with respect to so that the input torque of the system shown tends to become too great, the 'frietion. plate 'l'li tends to wind torque spring 18 still furtherby rotating on shaft 19 awayfrorn idler l4to'w'ard gear 2!. follower 16 to be driven so that its rotation on shaft 19 causes it to be partially withdrawn from frictional engagement with idler l4 against the torque of spring IS. The resultant time action is such that the friction force is self-reg ulating to a point just sufiicient to exceed the opposing torque of spring I8. This'action occurs independently of wear, aging, or coefficient of friction between idler l4 andfrictio'n follower plate IS, since the effect of changes in such constants is merely to change by a slight amount the position of follower H5 at whichit commences to disengage from idler 14. Since spring'lfi is p a relatively long helically wound spring',"t he -overall change in spring tension is veryslightfor small angular motion of the follower It with respect to shaft l9. The amount of angular motion is determined by the relative 'spe'eds'ofidler l4 and shaft :9 and by the pitch of the threads Thus, overdriveffol'n "idlei" I 4 causes 4 on shaft l9 and the follower. Normally, standard fine threads are used on these members, but changing the pitch of the threads within reasonable limits does not appreciably affect the operation of the device. 7

If the output gear 2'! or 31 is forceably restrained from rotating, slippage will occur between idler I4 and follower l6, and the torque delivered to gear 2| will be determined solely by the tension of spring I8.

"I'hus-it is seen that the force between the idler and the output gears is automatically controlled by the tension of spring [8, and that the torque delivered at the output gear 2| is constant regardless of the speed at which idler I4 is rotated.

It will be noted that the constant torque clutch ,above described is needed only because of the different speed and power requirements of the generator on the one hand and the clock work and arming rotor (which are described below) on the other hand. The generator, to meet 'very' exacting space and weight requirements, must be driven at high speed; the clock work must 'be' driven at low speed. This necessitates a high gear reduction ratio which means that when the wind vane is going faster than the clock work requires, large torque forces are set up which are difiicult to withstand without excessively heavy and rugged construction, and which also.

tend to drive the clock work faster than its norproblem of a suitable power source fora clock mechanism can be solved by directly coupling a wind vane or turbine to the clock gearing without the use of slipping clutch, and this too is within the purview of my invention. As shown in Fig. 10 the clutch may be eliminated "when there i no generator to' be driven, and the shaft may directly drive gear train 14 through gear 13.

. In this case the wind vane, other things being equal, will be'smaller and less powerful than in the previous case, andwill be pitchedto run at a speed only slightly higher than neededby the initial gear of the clock work, which will employ a smaller gear reduction than in the first case,

Gear 2i drives'escapement'pinion 22"which drives deadbeat escapement'23, 24 which'may.

be of the type commonly used in ordnance timers.

This serves to regulate accurately the timing].

of the arming. system which will now be described.

Small gear 37 which is fastened to gear 2i.

and rotates therewith drives large gear 38, to

which is fastened pinion 39, the two gears ro-.

tating freely,as a unit, on final gear shaft 4|.

Pinion 39' drives planet gear it to which .is 'fastened pinion 4?, the two gears, as a unit, being mounted physically on settable gear 44 by means of bracket 58 fastened to gear 44. This settable gear 44 is meshed with the internal gear teeth' of the setting'di'al 48 which 'surroundstheba'sei During the armingpycle and grounded by ear 58.

to the shaft 4| which carries arming disc 43. Thus, when the setting dial 48 and the settable geargM are stationary the output of the'clutch serves to turn the arming disc 43 through the ears as shown.

To vary the arming-time of the fuze the setting dial is is rotated, driving the settable gear 44 which carries with it the planet gear assembly. Since at this time gears 46 and 41 arenot'rotating, this motion of the planet gear causes the'arrningdisc '43 to rotate, thus changing the setting. 1

With the clock work in operation, when the arming disc 43 reaches the predetermined position corresponding to a preset time interval, finger 5'. on lock-out Washer 49 is-made to snap through notch 56 by the force of drive spring 53, and due to the engagementof the ear 58 (on washer 59) with detonator rotor 59, the latter is rotated approximately 90 into the armed position wherein contact 6!] on the rotor engages stationary contact 62 on insulating post 6211 which is supported by base plate 52, to provide a circuit through the detonator 6| to arm the fuze for detonation at a subsequent time by the electric element carried in space 9. This circuit is completed through contact 60a which is engaged At the same time the detonator is also aligned with booster lead 66 whereby booster 6! can be fired by the detonator to explode the projectile charge.

In the event that the fuze fails to operate for any reason, self-destruction is provided by an insulated contact 68 (Fig. 5) which is grounded by contact 69 mounted in the arming disc in such a manner as to close the detonator circuit several seccnds after the instant of arming. Contact 68 is supported from base plate 52 by means of post H, and insulated grommet 12. One arrangement of electric circuits is schematically shown in Fig. 9, although the actual circuit connections would depend on the type of electric fuze employed, and is a matter within the skill of any competent person versed in this art. In this figure the electric fuze would normally close the circuit to effect detonation is scrematically represented at S.

Since this timing mechanism is driven by an air turbine, it is necessary to take care of the time lag which may be introduced, in the case of a bomb, by the depth of the bomb bay, which, in a large plane may be as much as 16 feet. This, together with the normal time taken by the turbine to come up to speed, might result in a timing error of more than one second. To overcome this, the coil spring I8 of the constant torque clutch is made use of to provide approximately a one second prewind to the clock mechanism. This is done during assembly by manually rotating the follower friction plate I6 for approximately one or two revolutions on its screw thread, and locking it in place with the prewind ratchet pawl ll. The escapement is prevented from oscillating by means of a locking pin to be later released by the arming wire, in the case of a bomb, or in any other desired fashion. This prewind of the clutch serves two purposes. It eliminates the starting error mentioned above, and it completely disconnects the turbine and generator system from the arming system. The fuze then can be tested for electrical performance without any torque being transmitted through the clutch.

The prewinding of the torque spring I8 requires the gear assembly I9, 2|, 3! to be held against rotation until the projectile is released. This is accomplished by normally restraining escapement lever 2:! by means of a small soft leaf spring stop 3! (Fig. 8) riveted to. plate 2.9 and biased against lever 24 to restrain same against motion. Spring stop 3! is'normally restrained from engaging lever 24 by spring catch 32, which is stronger than spring stop 3] and normally keeps stop 3| away from lever 24 as shown in Fig. 2. A pivoted latch 33 is providedwhich, in the initial position of the unarmed fuze, disables catch 32 as shown in Fig. 8 so that stop 3| is effective to restrain lever 24. Insertion of arming pin, 38in hole 31 maintains spring catch 32 in the disabled state, but pivots latch 33 out of theway (as shown in Fig. Ba) so that it is henceforth inoperative. Withdrawal of the arming Wirewhen the projectile (in this case a bomb) is released, permits a spring (Fig. 1) to eject arming pin 36 which activates catch 33 to restrain stop 3l. This starts the clock mechanism, due to the prewind of spring i8, which threads shaft I 9 down relative to follower plate [6 (which does not move) until idler l4 engages the plate [6. Actually, friction follower plate l8 travels up on shaft l9 during this action until engagement with idler 14 occurs; by this time the turbine has come up to speed, as the bomb is out of the bomb bay into free air, and plate IE will drive the system as previously described, the direction of rotation being such that the pawl I! has no further effect.

It may be noted that even without the use of the ratchet pawl, this arming system permits testing of the electric system without effecting the time setting since the clutch design is such that when the escapement is held in a fixed position, this idler will automatically slip when the spring torque is exceeded.

Arming wire 15 may also be extended, as shown in Fig. 1, to pass through port 6 and into path of the turbine as an additional safety feature, or a second pin similar to pin 36 may be provided for this purpose if it is desired to insure locking of the turbine against rotation, the details of an arrangement for this purpose being within the skill of those versed in the art.

It will be seen that the above described conclusion accomplishes the objects of the invention but it will be apparent that other mechanical motions and elements than the ones shown could be used to accomplish the same objects within the scope of the invention as defined by the appended claims.

I claim:

1. An arming system for an electric fuze comprising a wind vane in the nose of said fuze, a shaft driven by said wind vane, a clockwork timer driven by said shaft, a powder train interrupter including an element movable from a safe position into an armed position, a latch for retaining said element initially in the safe position, spring means biasing said element into the armed position, means controlled by said timer for releasing said latch from said retaining position after a predetermined time of operation of said timer, and a high speed generator driven by said shaft for supplying power to said electric fuze, and a friction clutch between said shaft and said clockwork timer.

2. The invention as recited in claim 1, wherein said friction clutch is a constant-torque clutch.

3. The invention as recited in claim 2, wherein said clutch comprises an idler rotatably freely mounted on a threaded shaft and driven by said 

